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Old 11-10-2014, 09:30 PM   #41
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As far as I know for some of the new style packing mechanical seals such as the PSS... the carbon rides the stainless and it is a water free/dry seal...

When we were discussing old style compression packing...with at least the sorta new teflon packing...not even the really friction free stuff...even a drip can be eliminated by an amateur which is what I was with my old boat.

Lets not proliferate a myth that doesn't apply all the time.
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Old 11-11-2014, 12:10 AM   #42
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I am not the one proliferating myths...I have given you a technically based logical argument, read any text book on the topic, you will find they largely agree with what I have written, i didnt invent this stuff.....it is standard engineering practice

friction free however is a myth and friction when dry being the same as friction when lubricated (for any given material) is another

if you want to tighten your stern gland until it is fully dry thats completely up to you, however, proliferating that as "advice" is all i am cautioning against with a supporting explanation

finally, a pss seal will not perform satisfactorily if run dry.....why do you think they want the water supply (which started the post) ??? primary reason is to ensure the seal is operating in a lubricated condition
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Old 11-11-2014, 04:09 AM   #43
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If you have a stern gland with packing, as opposed to a mechanical seal, you should ALWAYS have a slight leak inboard. If you tighten the packing so as to entirely stop the leak you will wear your shaft. The "leak" lubricates the packing
Not really. With GFO packing you can run it dry. I've done it on countless boats and found the box will run nice and cool and there is no scoring of the shafts.
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Old 11-11-2014, 05:05 AM   #44
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I worked oilfield for 30 years or so and must have repacked a thousand centrifugal pumps, most used for drilling mud with a high viscosity and solids content. The "drip" used to be a spray within a few days requiring constant monitoring and tightening. About every 5 - 10 repacks, you would change the impellor, shaft and both wear plates as they were totally eroded. Then came the EPA with drip pans under each pump, expensive bromides etc and I guess someone decided to reengineer the decades old packing. Now they no longer leak although you still have the wear and tear on the inside of the pumps. So I think everyone is right, just perhaps not current. I sure don't believe they reengineered the packing for us sailors but we reap the benefit. I have it on my boat, monitor with a temp gun and have had no issues. I believe if I had a constant drip into my bilge I would change to the "dripless" system but as I am already "dripless", don't see the need.
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Old 11-11-2014, 06:47 AM   #45
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>in a conventional packed gland the same is the case, ensuring the packing is lubricated ensures it is operating with lower friction and this gives rise to less heat.

.I have given you a technically based logical argument, read any text book on the topic, you will find they largely agree with what I have written, i didnt invent this stuff.....it is standard engineering practice<

The hassle is the new material has so little friction DRY that no heat rise is created

Folks with heat guns see the shaft temps Drop after the change from flax or teflon.

With no need for a cooling flow the grit in the lube water does not get between the packing and shaft , where it gets imbedded in packing and scores the shaft.

I have no idea of the Duramax would run cooler , if it was set up to drip underway ,

but since most operate at local water temp, who would care?
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Old 11-11-2014, 09:26 AM   #46
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Mate here's my PYI PSS. it came with the hose nipple. The "vent" is so you don't need to burp it. Going to or around 12knots doesn't require water injection.

Don't over complicate it.

IMHO, I would be more concerned about the collar and the clamps. When i bought the seal I immediately removed the worm screw clamps and fitted t bar clamps and fitted the shaft retention collar.

They are more critical than a breather line that is redundant at your speeds.

Im still building the boat so can't comment on the performance of the product, just what I've learnt

Hope it helps.

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Old 11-11-2014, 10:05 AM   #47
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I worked oilfield for 30 years or so and must have repacked a thousand centrifugal pumps, most used for drilling mud with a high viscosity and solids content. .
Same for me but in mining related processing applications, with pumps as big as 5000 hp. The amount of slurry released by a "standard" packing system was so large that dripless systems with filtered "fresh" water for lubricating the gland seal became common if not mandatory decades ago. When dealing with corrosive slurries a drip at the gland is not acceptable so dripless systems utilizing all manners or seals came to be.

A properly installed dripless system is not a new design and like anything on a boat requires watching and acceptable access. Ditto duramax or hemp!

Delfin, did your shaft show any problems on your recent haulout? If not it seems your system is not suffering from stagnant water related ills. But when parked at the dock several useful approaches have been noted. Salt water intrusion into a very nice steel hulled boat though is not something I would do on a routine untended basis, maybe just once every few days and done manually into a shower sump??
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Old 11-11-2014, 10:13 AM   #48
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Originally Posted by psneeld View Post
As far as I know for some of the new style packing mechanical seals such as the PSS... the carbon rides the stainless and it is a water free/dry seal...
The PYI seal depends on a water interface between the carbon ring and the sealing plate for lubrication. It is only a few molecules thick, but it is there. There is no drip because this water gasket has no flow. The vent, if used as a point of water injection pushes water into the stern tube, not between the carbon and the seal. The system is burped when you first launch to get the air out and to get the water gasket established. After that the main reason to inject water, according to PYI, is if the boat is moving fast enough to create negative pressure at the stern cutlass bearing that would cause evacuation of the water in the stern tube. The secondary reason that we've discussed is to have a slow flow of water to purge contaminants out of the tube to reduce wear on the bearings, which is why I've decided to plumb a line from the through hull to the vent - a practice PYI said was not uncommon for the reasons stated.
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Old 11-11-2014, 10:15 AM   #49
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Mate here's my PYI PSS. it came with the hose nipple. The "vent" is so you don't need to burp it. Going to or around 12knots doesn't require water injection.

Don't over complicate it.

IMHO, I would be more concerned about the collar and the clamps. When i bought the seal I immediately removed the worm screw clamps and fitted t bar clamps and fitted the shaft retention collar.

They are more critical than a breather line that is redundant at your speeds.

Im still building the boat so can't comment on the performance of the product, just what I've learnt

Hope it helps.

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Hendo, if you read your instructions you will see that you definitely need to burp it on splash. The yard didn't the first time I launched and after around 2 minutes of run time the squeal from the shaft on the dry cutlass bearings was pretty horrendous. The vent was clear but for whatever reason, the stern tube had insufficient water in it.

Burp the baby.
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Old 11-11-2014, 10:39 AM   #50
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Same for me but in mining related processing applications, with pumps as big as 5000 hp. The amount of slurry released by a "standard" packing system was so large that dripless systems with filtered "fresh" water for lubricating the gland seal became common if not mandatory decades ago. When dealing with corrosive slurries a drip at the gland is not acceptable so dripless systems utilizing all manners or seals came to be.

A properly installed dripless system is not a new design and like anything on a boat requires watching and acceptable access. Ditto duramax or hemp!

Delfin, did your shaft show any problems on your recent haulout? If not it seems your system is not suffering from stagnant water related ills. But when parked at the dock several useful approaches have been noted. Salt water intrusion into a very nice steel hulled boat though is not something I would do on a routine untended basis, maybe just once every few days and done manually into a shower sump??
Thanks Tom. The shaft was fine. Run out was less than .002 as I recall - not enough to worry about according to Townsend Bay Marine. It was actually Paul Z, manager of the yard, who made the recommendation that I "think" about water injection. The concern was not the shaft but the cutlass bearings, where detritus would increase wear. They only lasted 5 years, so I think there is reason to be concerned.

I asked about corrosion from introducing oxygenated water and was told by PYI that it wouldn't be an issue, as did the yard. The capper for me is the vent tube, which I consider the weakest part of the entire system. If it failed, you would have a 1/8" hole in your boat. Not something the bilge pumps wouldn't handle, but still. Given that, plumbing it into the through hull, which I always close on leaving the vessel, seems like a no change situation, flooding wise, but an improvement in longevity of the cutlass bearings. I have read about systems for coating the inside of the stern tube, but every time I have asked a yard they give me blank stares.

Paul Z at the yard also told me something I really wasn't aware of, but seems to be true. He said that sea water a couple feet down has so little oxygen in it anyway that the corrosion rate is minimal. Didn't seem right to me, but we had one area where I had to move the through hull to accommodate the stabilizers and it caused a failure of the epoxy barrier coat around 4 feet under the water line. Scratch at it with your finger, and you can reveal essentially uncorroded, but unprotected steel, so I think he is right, at least in our cold PNW waters.
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Old 11-11-2014, 01:28 PM   #51
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The PYI seal depends on a water interface between the carbon ring and the sealing plate for lubrication. It is only a few molecules thick, but it is there. There is no drip because this water gasket has no flow. The vent, if used as a point of water injection pushes water into the stern tube, not between the carbon and the seal. The system is burped when you first launch to get the air out and to get the water gasket established. After that the main reason to inject water, according to PYI, is if the boat is moving fast enough to create negative pressure at the stern cutlass bearing that would cause evacuation of the water in the stern tube. The secondary reason that we've discussed is to have a slow flow of water to purge contaminants out of the tube to reduce wear on the bearings, which is why I've decided to plumb a line from the through hull to the vent - a practice PYI said was not uncommon for the reasons stated.
I have one on the assistance towing boat and have been using it and repairing it for 12 years.

I couldn't locate whether there was a water layer or not, I thought if it were a decent carbon seal it wouldn't need it as some mechanical seals don't.

But the point is whether carbon against stainless or Teflon against a stainless shaft...the water layer needs only be enough to keep friction at bay....not necessarily a drip and that's all I was pointing out from the beginning.
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Old 11-12-2014, 03:03 AM   #52
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Hendo, if you read your instructions you will see that you definitely need to burp it on splash. The yard didn't the first time I launched and after around 2 minutes of run time the squeal from the shaft on the dry cutlass bearings was pretty horrendous. The vent was clear but for whatever reason, the stern tube had insufficient water in it.

Burp the baby.

Ok I'll burp it but only cause you said so mate 👍


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